Daniel Matheson Adams MD, Presenter: Nothing to Disclose

Scott Stevens MD, Abstract Co-Author: Researcher, Iverson Genetic Diagnostics, Inc

Scott Woller MD, Abstract Co-Author: Nothing to Disclose

Joseph Bledsoe MD, Abstract Co-Author: Nothing to Disclose

Todd Delton Lovelace MD, Abstract Co-Author: Nothing to Disclose

Scott Evans PhD, Abstract Co-Author: Nothing to Disclose

Jim Lloyd BS, Abstract Co-Author: Nothing to Disclose

Valerie Aston RT, Abstract Co-Author: Nothing to Disclose

C. Gregory Elliott MD, Abstract Co-Author: Nothing to Disclose

Compared to original trials which derived pre-test probability systems for suspected pulmonary embolism (PE), the prevalence of PE at each given level of pre-test probability has decreased. Consequently, higher values of d-dimer may safely exclude PE in suspected cases. We therefore examined the implications of increasing the d-dimer threshold for patients with decreasing clinical pretest probability.

Consecutive CT pulmonary angiography (CTPA) exams performed for suspected PE over a 14 month period were retrospectively identified and final interpretations were recorded. Data to calculate the Revised Geneva Score (RGS) for each encounter were extracted from the electronic medical record by electronic means and manual review, and d-dimer values were collected. All patient encounters for which pretest probability was calculated as low (RGS 0-3) or intermediate (RGS 4-10) and for which d-dimer testing was performed were included in the study. The prevalence of PE for low and intermediate probability patients with d-dimer values below adjusted thresholds was then determined.

Of 3500 CTPA exams performed, 1745 involved encounters for patients with low or intermediate probability and d-dimer testing performed. The remainder included 167 with high probability, and 1588 with low to intermediate probability and no d-dimer testing performed. Intermediate probability patients had a slightly higher mean age (53.2 vs. 50.1 years, p=0.001), but there was no significant difference in the prevalence of PE for low and intermediate probability patients at d-dimer levels below 1000 (3.7% vs. 2.5%, p=0.29). For both groups combined, prevalence of PE remained below 2% with a threshold of 700 (1.8%, 95% CI 1.1-3.1%), which accounted for 41% of the CTPA exams.

Prevalence of PE is not significantly different between patients with low and intermediate pretest probability at d-dimer levels below 1000. Prevalence of PE remains below 2% for all low and intermediate probability patients below 700, and 41% of the CTPA exams could be avoided if this level was used to exclude PE. Prospective management studies to select the optimal adjustment of d-dimer are necessary before clinical implementation may occur.

CTPA utilization could be substantially reduced if d-dimer thresholds were increased for exclusion of PE for patients with both low and intermediate pretest probability.

Adams, D, Stevens, S, Woller, S, Bledsoe, J, Lovelace, T, Evans, S, Lloyd, J, Aston, V, Elliott, C, Implications of Increasing the D-Dimer Threshold in Patients with a Lower Pretest Probability to Exclude Pulmonary Embolism prior to CT Pulmonary Angiography.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14014603.html